Severe vibration problem plagues moon rocket design

MARK CARREAU, Copyright 2008 Houston Chronicle

Published 6:30 am, Saturday, January 19, 2008

Experts at NASA are wrestling with a propulsion system problem in the design of the new moonship that would create dangerously high vibrations for the spacecraft and its astronauts, the space agency said Friday.

Officials said in a statement that they expect to develop by March several options to address the problem with the Ares I rocket, which is in the early design phase.

NASA is counting on the Ares I rocket and the Orion crew capsule attached to it to replace the aging space shuttle, which is facing retirement in 2010.

At current funding levels, NASA hopes to begin launching astronauts to the international space station aboard the new moonship by March 2015.

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Serious problem

The vibration problem was first disclosed on Friday by NASA Watch, an Web site focused on space agency issues.

NASA officials declined requests for interviews on Friday, but spokeswoman Beth Dickey provided a lengthy statement that identified the problem as "thrust oscillation," an issue that was discussed by the moonship's development team in October during a design review.

The statement characterized the problem, which was revealed in computer modeling, as a pulsing of the thrust late in the burn of the rocket's first stage.

"These longitudinal forces may increase the loads experienced by the Ares I during flight, and may exceed allowable loads on various portions of the vehicle and allowable forces on the astronaut crew," the statement said.

Program managers assigned the seriousness of the problem a "four" on a risk scale of five and have called on experts from outside of NASA as well as inside the agency for assistance.

Confident in solution

"This is a development project like Apollo. I hope no one was so ill-informed as to believe that we would be able to develop a system to replace the shuttle without facing any challenges in doing so," Griffin said in a separate statement. "NASA has an excellent track record of resolving technical challenges. We're confident we'll solve this one as well."

The Ares I first stage is a longer version of the shuttle's solid rocket booster. The upper stage is comprised of an upgrade of the Apollo-era rocket engine.

Normal design kinks

Thrust oscillation is a phenomenon found in all solid rocket motors, including the two used to power each launch of the space shuttle.

"It is a well and long understood phenomenon in the launch industry," said George Torres , a spokesman for ATK. "Many other launch vehicles at this stage of development have had to deal with this issue and have dealt with it as a normal part of the development process."

Four years ago, President Bush directed NASA's return to the moon with astronauts by 2020.

As part of the directive, Bush instructed the agency to retire the shuttle as it completes the assembly of the space station.

On Dec. 12, NASA awarded the last of the contracts for the development of the Ares I rocket and Orion capsule, a committment of $13.6 billion.